This Is Why You Should Never Read Science From Regular News Media

March 18, 2014

Because they screw it up and spew misinformed drivel like Salon does. If they would have done a modicum of research, they would have found out the discovery is the sign of a gravitational wave embedded in the cosmic microwave background. This is more about the evidence for Alan Gurth, Andrei Linde, etc’s inflationary model, which covers up some of the unsolved gaping hole left by the big bang theory. Yes, the article does talk about the fact that it confirms inflation, but they always mix the facts up with some misinformation. As of yet, there hasn’t been any direct observation of gravitational waves. Not that it matters much because gravitational waves have been confirmed by indirect observations before even this one.  For example, by observing two neutron stars orbiting close to each other, they have found behavior that matches those predicted by the existence of gravitational wave. Seriously, research! Or am I asking too much for a reporter these days?


Rare Snapshot of Rapidly Evolving Star

March 12, 2014

This is filler for my next post in star death, but thought I should show you something relevant to stellar evolution. This one is a yellow hypergiant, in fact, the largest yellow hypergiant discovered. Yellow hypergiants are one stage of a 25 plus solar mass star, and they are very rare. One of the great things about this one is that as decades went by, the swelling and cooling of the star was noticeable. That rarely happens over human lifetimes, as changes in stars happen over millions or billions of years. Another fascinating thing is that the star swelled so large that it is pretty much touching its smaller binary counterpart. I don’t know how exactly this will play out, but as the article says, it will probably affect how the star evolves in the future.


Star Endings: Electron Degeneracy End

February 19, 2014

Introduction

Welcome to my next series of posts, which is about all the way stars die. You see, depending on the mass of the star, they can have very different “endings”, sort to speak. So don’t believe anyone who tells you that the sun is going to explode or something like that. It won’t. Instead, something else is going to happen. There are a lot of caveats as to how this works, and as you will see in another post, mass is not the only factor in how a star ends up. Also, each endings have sub endings, the universe is quiet complicated after all. What I will not be going into is the details of the evolution of the stars. Just their deaths. The posts would be really long and meandering with those details included, so I will be very general instead. Believe me, there are a lot of ways stars evolve and the intricacies are enormous. Now that you know what you will be getting, let’s begin.

The Basic Working of a Star

In order to understand how all stars die, one has to understand the inner workings of a star. All stars are fueled by the fusion of atoms in its interior. During their main sequence phase (the relatively stable, long lived part of a star’s life), hydrogens are fused into helium. When it does so, a little bit of the mass of the atoms are converted into light, E=mc^2=pc, Einstein’s famous equation (Wait, pc? What the hell is that, you might be wondering. That may be a topic for another discussion, but the energy due to mass m turns into the energy due to momentum p of light). Incredibly, the sun loses millions of tons every second to this process. And in fact, the mass of the four protons used to produce helium are a little bit more than the mass of helium.

During that main sequence period, the thermal and radiation pressure from a star’s interior counterbalances the gravitational force trying to squeeze the star. So long as that hydrogen in the sun’s core keeps fusing, the truce is maintained, and the star keeps chugging along without agitation. But as we all know, resources don’t last forever. What happens when the hydrogen, or at least the really hot hydrogen in the center that are able to fuse runs out, and all that remains are useless helium and hydrogen? That is when all hell breaks loose, and the differing mass of the stars will send them into wildly different paths.

Electron Degeneracy Pressure

One fundamental concept I want to get to before going into what will be the remnants of the dead star is the concept of degenerate matter. Aside from being a really cool sounding word, it is the stuff stars will eventually be made of. They are highly compressed form of matter, squeezed to such an extent that quantum mechanical properties take over classical mechanics. In degenerate matter, pressure does not depend on temperature. What happens instead is that if you dump mass on it, instead of getting bigger, pressure increases and the whole thing becomes smaller and denser. They are strange kinds of matter indeed, and neither solid, liquid, gas, nor plasma quiet describes what this is. It is another state of matter.

What causes this phase of matter at extreme high pressure is the fact you can’t just keep squeezing things infinitely without running into a snag, which is the rules of quantum mechanics. In the case of electron degeneracy, it is the fact that electrons have to keep filling lower and lower energy levels. According to the Pauli Exclusion Principle, no electrons shall occupy the same quantum states. So for example, two electrons can’t be in the same energy unless their spin number is different (in quantum mechanics, spins are rotations that look like it exists, but really isn’t there, yeah, it is kind of confusing). Since there are only two spin numbers, positive and negative, if you try to squeeze one more electron into the energy level, the particles will resist the other electron from moving in. That creates the pressure needed to resist the compression.

Now, considering the extreme gravity of a ball of super high density stuff, the pressure needed to hold the degenerate matter must be enormous. The counteracting electron pressure is caused by the momentum of the electrons heavily affected by the uncertainty principle, which is the prime characteristic of quantum physics. The uncertainty principle says that you can’t measure position accurately without creating uncertainty with momentum and vice versa. So, since objects in degenerate matter are very tightly packed, the position becomes very certain, but the momentum becomes extremely uncertain. Which means that there is a probability that collectively, momentum will be high enough to resist the strong gravitational force that threatens to collapse the matter. Now you can see why increasing temperature does nothing. The force involved is too great for temperature to increase electron pressure in degenerate matter. Also, at that scale, the uncertainty principle is the dominant factor at play.

As you will see in a later post, even as electron degeneracy pressure fails, there will be a fail safe that particles will rely on to make sure the rules of quantum mechanics is respected. When even that fails, well, they commit the most dramatic suicide in the universe. At the point before 10 solar mass stars, though, electron degeneracy will prevail, and what remains after everything is over are hot corpses called white dwarves. These are extremely dense, exotic objects in which an object the size of planet Earth can have the mass of the sun, and it is what will remain after the end of these low massed stars.

Convection End

For stars below 0.5 solar mass, the action in the middle layer of the star, between the surface and the core, becomes extremely important. Take a look at the following diagram of the interior:

(source of image)

The circular arrows represent convective zones while the squiggly arrows represent the radiative zone. They represent the different ways in which energy moves outside. In radiative zone, light bounces around from atom to atom, taking on average over 170 thousand years to leave it. In the convection zone, the plasma moves by convection towards the top, being less dense due to the higher temperature at the bottom, and when it reaches the top, it releases the light energy. Now, notice how red dwarves, to the left of the diagram, consists almost entirely of convective zones? This means that even as the hydrogen is used up in its core, the convection ensures that fresh materials from the top reaches down to the bottom. Combined with having so much materials to work it, and the much slower pace of reaction compared to the more massive stars, red dwarves will get to live for trillions of years to come. Which means that the end of their lives has never been observed, and details on how they might die are mostly theoretical. Nevertheless, let’s speculate, shall we?

Red dwarves, after their extraordinarily long lives, are theorized to die quietly. Like all stars, they will grow brighterThe lower massed ones won’t expand into a red giant due to it not being opaque enough. Instead, they will grow brighter and brighter and change colors and probably reach yellow to white. Eventually though, the hydrogen will run out and all that will remain is helium. Unlike all other star deaths, there will be no fireworks accompanying the fuel shortage. Red dwarves aren’t massive and hot enough to fuse helium into carbon, and due to how the convection mixes up the materials, there won’t be any hydrogen shell to fuse around the helium. The gravitational force will overcome the outward pressure and the star will compress into a helium white dwarf. Or at least that is what is believed the future of a red dwarf star is.

Planetary Nebula End

Above 0.5 solar mass, stars will be able to go on further with the nuclear reactions. They will swell many times their size as their luminosity increases significantly while the star ekes out a reaction from the bits of hydrogen around the helium core when the core was compressing. Later the core will ignite its helium and turn it to a carbon/oxygen core. Finally, when the helium runs out, another compression of the core will ignite the helium shell around the core. As shell helium fusion turns on and off due to running out and then being repleted by the fusion of hydrogen above it, a thermal pulse causes a huge chunks of the hydrogen envelope of the star to be blown away. The star will blast away layers after layers of plasma over periods of tens of thousands of years, creating gas envelopes around the core, the materials speeding away. This is how the sun itself will die. The end result is this:

(source of image)

 The core that remains will shine extremely hot with ultraviolet, stripping off the electrons from the gas and  causing the gas to glow. This is the so called “planetary nebula“.  If it is going to go out, might as well die beautifully, right? Over time, the gas dissipates and all that will remain is the carbon/oxygen electron degenerate matter, the most common form of white dwarves. The stars with 8 to 10 solar masses will get the chance to fuse carbon and get an oxygen/neon/magnesium core. You might think that after this, there will be higher masses in which more opportunity to fuse atoms occur. Yes, they do, but in terms of electron degeneracy, this is where it stops.

Fate of the White Dwarves

Even after the fusion stops and all that remains is the white dwarf, the star will keep shining on gloriously for a long time. Degenerate matter is a perfect conductor of heat, and the glowing you see is the heat stored in it. It starts out tens of thousands of degree hot and over time cools down. Eventually, the white dwarf will seize to be visible, and a very long time after that, stop emitting heat. Such an object, the black dwarf, does not exist yet because the universe is not old enough to have it cooled down, but it is the most likely outcome.

Now, the electron degeneracy scenario might work for the stars less than 10 solar masses, but what happens to star around and above that? What happens when the core gets so massive that electron pressure is not enough to hold up the core? Will electrons get to occupy the same quantum state? No, as hinted previously, particles like electrons hate being in the same quantum state and it will do everything it can to avoid that. For these massive stars, the core collapse ending is what awaits them, and interestingly, the explosion of a white dwarf is possible through such a mechanism. This will be the subject of the next post.

Sources and further reading materials:

http://imagine.gsfc.nasa.gov/docs/science/know_l2/stars.html

http://ircamera.as.arizona.edu/astr_250/Lectures/Lec17_sml.htm

http://solar.physics.montana.edu/ypop/Spotlight/SunInfo/Radzone.html

http://solar.physics.montana.edu/ypop/Spotlight/SunInfo/Conzone.html

http://onlinelibrary.wiley.com/doi/10.1002/asna.200510440/pdf

http://iopscience.iop.org/0004-637X/482/1/420/pdf/0004-637X_482_1_420.pdf

http://www.universetoday.com/18847/life-of-the-sun/

http://www.atnf.csiro.au/outreach/education/senior/astrophysics/stellarevolution_deathlow.html

http://www.universetoday.com/44836/unusual-massive-white-dwarf-stars-have-oxygen-atmospheres/


Planet of the Day: Kepler 413b

February 9, 2014

This planet is a wild one. The planet has been found to precess  around 30 degrees in less than 11 years. Some of you may wonder what precession is. Well, basically it is the wobble of an object as it rotates. It happens to tops, and it does indeed happen on planet Earth too. There are various forms of precessions. The planet’s angle of rotation could change, which Kepler 413b does extremely quickly, and like the top, the axis of rotation itself could rotate in a circle. The planet Earth though, precesses so slowly that you need to wait thousands of years so you can even begin to see the change of the positions of the stars. Not in the case of this planet, wobbling without any stability.

There are also the orbital kind of precessions. Before going further, you should be aware that all orbits are ellipses, with the center of mass at a focus. Meaning, the orbits are not perfect circles, more like ovals, and the center of mass is not in the perfect center of the oval, but offset by a specific mathematical amount to a place called the focus. This means that in the case of orbital precession, the shape of the oval rotates around the focus itself over a large period of time. Mercury is famous for having a large orbital precession, caused by a combination of the gravitational pull of other Solar System objects and the mechanics of general relativity (aka the most accurate theory of gravity yet) itself.

The case of this planet is odd, though. When they first detected the planet by observing that the brightness of the star fell, signifying that the planet went in front of the star. They observed further cycles of the planet moving in front of the star. At one point, though, no object blocked the star’s light. And it kept going like this for many days until once again, they detected the same planet blocking the star’s light again and again. The significance of this discovery is compelling. It means the orbit is wobbling up and down, at times having the planet move in front of the star, at times above or below it.

The combination of all those factors would make seasonal changes of this planet extreme and unpredictable. As for what could have cause this? At this point, any theory about what happened would be speculation. We just don’t have enough data. The link itself gives plausible scenarios, though.

As for the physical characteristic itself, it is a gas giant. It is really close to its parent star, making its temperature very hot. It is 65 times the mass of the Earth, making it many times more massive than Neptune, but less massive than Saturn. While this goes in line with other gas giant discoveries, that its behavior deviates so much from what we have seen other planets do in their spin and orbit makes it a noteworthy object of study.


The Waters of Ceres and the Jet Plumes of Water

January 25, 2014

Using the Herschel Space Observatory, a far infrared and submillimeter (between far infrared and microwave) telescope, astronomers have detected water around Ceres.

Ceres is the dwarf planet that resides in the asteroid belt, making it the largest object in the area. For those of you who just heard about Ceres, it is not new. Back when it was discovered in 1801, it used to be a planet. Then after a slew of discoveries in the asteroid belt like Vesta, Juno, Pallas, they decided that they were different enough to be labeled asteroids. Then came 2006, and due to discovery of an object larger than Pluto, Eris, and other large Kuiper belt objects, they changed the definition. Ceres was upgraded to the status of dwarf planet because it was round, and revolved around the sun, but did not count as a full planet because it failed to clear the orbit, which is clear since Ceres resides in the asteroid belt.

Now the question is, how did the water get there from Ceres? Well, it is thought that whenever Ceres gets somewhat closer to the sun in its orbit, a jet of water is released in certain areas. The reason they believe that is that the four times they observed Ceres, they didn’t see any water signature once. Not only that, as it was rotating and moving along the orbits, the signals changed, and they believe the likely area of emission are dark spots that they have observed on the surface. While they aren’t sure about this a hundred percent, once the space probe Dawn arrives, they will be able to confirm their findings.

The really cool aspect of this discovery is the blurring between asteroids and comets. Comets are icy objects, and they are the ones that release jets of water vapor. While Ceres itself is more asteroid like, more rock like, its mixture with ice gives it a comet like behavior sometimes. So overall, Ceres has a mix of really interesting features. It is large and massive enough to be planet like, it has asteroid like compositions, and it has its icy bits like comets.


Planet of the Day: The Three Planets of M67 Cluster

January 24, 2014

First of all, yes, 3 planets doesn’t count as a “planet”, singular, I know, but it sounds better this way… Whatever, on to the topic.

While this is not the first time, it is pretty cool that three planets have been found in an open cluster. This one is called the Messier 67. Open clusters are group of stars numbering in the thousands that are born from the same gas cloud. So for example, Orion Nebula may one day be an open cluster! Anyways, these open clusters eventually dissipate and the stars go on on their own. As for why this is important is the fact that crowded open clusters are believed to be planet unfriendly. That doesn’t mean it is impossible, but it does mean that finding some make them quiet special and fascinating to study at.

All three planets are gas giants. They were found by measuring the wobble of the parent star with the Doppler Shift. While we may not exactly know their size, we know their mass. They are 0.34, 0.40, and 1.54 times the mass of Jupiter. Let me remind you, of course, that all scientific measurements have uncertainties, and the one for the third one is particularly large, plus/minus 0.24. Interestingly, two of them orbit around sun like stars, although slightly less luminous than the sun (sun has luminosity 2, these two stars have luminosity 5). The planets themselves, though, orbit too close. They are the hot Jupiter varieties, and there is nothing like them in the Solar System. That similarity and contrast is what makes those planets very interesting. The planet more massive than Jupiter, on the other hand, orbit a giant star, but farther away. This one has what one might say a more reasonable orbit.

Other than that, there is not much more to say. They happen to be pretty cool because they were found in tight open clusters. You can look at the study, if you want all the nitty gritty details. You can also get a good summary from Universe Today here.


Planet of the Day: KOI-314c

January 16, 2014

KOI-314c is a recently discovered Earth massed planet. Its density is also quiet low considering that the planet’s diameter is 1.6 times the Earth. It was discovered using the Kepler telescope, which detects the dimming of a star as the planet orbits in front of it. The press release I linked above has tons of information about it. Badastronomy also has a great general summary here.

Speaking of planets larger than the Earth, but smaller than Neptune, the most common types of planets to be discovered seems to be those. Thanks to Kepler, we are getting a better idea of the size distribution of planets, at least those that orbit close to the star. Of course, the planets are not going all going to be of the same density. Some might be rocky, others could be icy, and it could also be gassy like Neptune. Based on the measurements of the densities, most of them seem to be the gaseous kind. Another noteworthy point about this discovery is that the Solar System has no planet of this kind even though it is extremely common in the universe.  Of course, this doesn’t make the Solar System special, it just got the way it is by the laws of physics and chance. Still, it is a cool fact, and it shows how diverse star systems and planets are.


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